I know a lot of you are waiting for a report on the Imperial SO I'm building and a comparison to the standard Imperial. I got the first Imperial SO up and running, but what a disappointment! Something is wrong! I'm hoping someone can figure out what it is, because I can't imagine what could cause such a severe problem. If I had to guess I'd say the speaker back radiations are contained in the sealed compression chamber (like they should be). And the speaker front radiations are being delayed 180 degrees by the horn so the horn and the speaker are out of phase with each other and canceling big time. I can pump a lot of watts into this thing and no sound comes out. Here are 3 pictures that, I hope, show someone what it is that I did wrong (are you out there Steve?)http://www.mninter.net/~kuechle/impso_1.jpg

Disregard the blue line on the graphs, its the green line that has the information.

Graphs 1 and 2 compare the new Imperial SO to the standard Imperial when driven with a sine sweep. The peak amplitude is 10 db down for the Imperial SO, which might not be too unexpected as we are comparing 1 speaker to 2 speakers, but at 30 hz the Imperial SO is 24 db down from the standard Imperial. Whats up with that?

Graphs 3 thru 7 all have the same, lower volume, sine sweep input. 3 is the Imperial SO as it should be. 4 is with the front cover removed. This is the board with the Karlson shaped slot in it. According to the graphs, this K-slot makes no difference at all! 5 is a picture of what happened when I covered up the K-slot with a solid board...higher volume by 6-7 db across the frequency range, but that nasty steep slope (looks like almost 30 db/octave to me) is still there from 20 all the way to 50 hz.

Graphs 6 and 7 are with a different speaker...pretty much the same results.

Well, I'm open to suggestions. Right now I'm thinking how hard is it going to be to turn these guys into a second pair of standard Imperials?

Wow that is not what I expected my "SO" works pretty goodI will look at the pics and info later and compare it to my Hack version. I will say that mine does not have that boom that everyone associates with "bass". Mine does seem to require more power but not a whole lot more. I attributed it to a cheap car sub.

I will take a look at it later. I am just getting a start bulding a small light table out of a trashed 17 lcd monitor. thought I would check in. Not so good buddy! got to be something simple.

Hey! Its a little hard to figure things out when I have not built a real ImpSO. I cannot believe it is performing that bad. Maybe its a lot of little things that all together is causing grief.But I doubt it by looking at the pics. It looks pretty good to me.but here I go without a clue.

1.below the bottom of the dirver where it meets the front face that has the Kslot is it tight and no air blowing past.

2. at the top of the driver where the beginning of the mouth. is it big enough ( to steves specs) I think mine is close to 4 inches.

3. the slot is huge compared to my version the points are correct but the curve is pretty big compared to mine.What I am trying to say is the opening is too big?

4. of course your sealed chamber is not leaking air5.The driver your using is designed for a sealed enclosure?

the driver is good and wiring etc etc. Did you try to swap dirvers?

I don,t think your feeding ( loading the horn) enough. and the imbalance is creating the cancellation. Or that is the only thing I can come up with.I can't imagine that you did anything wrong to be honest. and Steves design is considerably differant than mine.however I used a 12" driver and changed the dimensions and modified a Imperial corner cab

I don't think I was much help at all, but maybe I can spark a new train of thought at the very least.

Good luck and give Steve a call before you give up. sometimes if you walk away for a day or two it will come to ya.

In my opinion the K-slot seems a bit large. It doesnt give the loading it should. It should direct some pressure into the horn and equalize the pressure seen by the back and front of the driver.You have probably checked that the sealed chamber is airtight but it never hurts to do that again. Especially for leakes into the horn.

Just a couple of responces: 1) I am working from the standard Imperial plans, the first look picture Steve posted a while back, a sketch Steve made for me at Decfest 2005 showing the differences, and a bunch of pictures I took of Steve's Imperial SO's. 2) Everything is sealed properly and not leaking. 3) The front board with the K-slot has a gasket under it so it seals correctly with the compression chamber. 4) I have tried 2 different, working, speakers from 2 different manufactures. Results were the same. 5) I agree the K-slot seems big, but covering up parts of it doesn't seem to make much difference...hell removing the slot entirly makes no difference, and covering the slot completly does increase the output but does nothing to reduce the terrible steep rolloff below 50 hz.

Heres a question for you guys: In the standard Imperial the output of the horn and the output of the front of the speakers MUST be in phase. The only way to do this is for the horn to add an additional 180 degrees of phase shift to the back rediations of the speaker giving 360 degrees of total phase shift. In the Imperial SO the horn hasn't changed, so it is still probably adding 180 degrees of shift. Where are the other 180 degrees of phase shift comming from? The k-slot? - I don't see how. Is there a design flaw here?

[quote author=dank link=1129662594/0#6 date=1129735892] ......................... Heres a question for you guys: In the standard Imperial the output of the horn and the output of the front of the speakers MUST be in phase. The only way to do this is for the horn to add an additional 180 degrees of phase shift to the back rediations of the speaker giving 360 degrees of total phase shift. In the Imperial SO the horn hasn't changed, so it is still probably adding 180 degrees of shift. Where are the other 180 degrees of phase shift comming from? The k-slot? - I don't see how. Is there a design flaw here?

DanK [/quote]

This assumption is flawed because the original Imperial uses a vented chamber AND the horn to increase efficiency. The actual phase of the output of the horn will be different at every frequency. The horn loaded vent is so efficient that the direct driver output is almost insignificant in the bottom octave and so the phase difference between the two is also insignificant.

What happens if you correct the slot dimensions and put 2 watts or so on it and compare it to an efficient full range speaker, instead of another Imperial?

A wild thought crossed my mind.What about making the sealed chamber a vented one instead.Say tuned to 18 - 20 hz with the vents fireing into the very beginning of the horn, but with the open "coupling" of the Imp SO ? ??? ??? ???That will say, keep the K-slot and everything like it is now but put 4 tubes/vents from inside the previous sealed box, that fires into the horn. That should still only excite resonanses in the horn in the lowest octave and filter away everything else.That would probably retain the high efficiency, or at least partly.(?)

I am almost finisihed with the SO plans. They will also include some pics of the actual speaker with the front panel removed. I would hang on until I get at least the pdf file done and see what you can do to get yours a bit closer. At the same time, what size and type box did the computer model for each of the two drivers you selected? You need to find drivers that will hit 25Hz a sealed box of around 5 cubic feet.

Mine was 4 cubic feet @ 27 HzI used a sealed chamber and no vent. I was going to use a bass relex Square port into the horn, when I started designing it. I went with a basic karlson with a Imperial horn instead.

I really would like to see a real one, Still like to build one. I am not in a hurry because My hack works well. I would like a driver with a higher sensitivity instead of 86Db for my first change.

I disgarded the port loaded horn because something JohnF said a while ago. wish I could remember where in this forum it was.

Well, just when you start to think you know something about this field of science something happens to remind you that you really don't know much of anything at all. After playing around with the size of the k-slot for a couple hours I decided that there was no tuning involved. It simple doesn’t matter. The only thing that made any difference at all was covering up the slot completely. So, I covered it up. Now all the energy is going into the horn. It sounds ok, not as good as the standard Imperial, but ok. Then as I was moving things around and swapping Imperials in and out I happened to face the boarded up Imperial SO into the corner while it was playing. Wow. +10 db instantly. Clear as a bell. Effortless bass. I then tried facing a standard Imperial into the corner, just barley an audible improvement, no where nears as much as with the Imperial SO. One boarded up Imperial SO facing into the corner is sounding better than my pair of standard Imperials. That’s one 18” speaker smoking four 18’s. I’m rethinking my system now. Perhaps more is not always better.

The speaker I’m using doesn’t seem to model well in a sealed 5 cubic foot box (if I’m using the s/w correctly). Perhaps some nice person out there can check my results to see if I’m doing it right. Fs = 30.5 hz, Qts = .227, Vas = 8.6 cubic feet, 8 ohm, 18” diameter. I was under the impression that the high Fs / Qts (30 / .227 = 132) makes it a very good horn driver. When I model it in a sealed box of 5 cubic feet my s/w says Fc = 50, Qtc = .37 and Cutoff(F3) = 116. It also gives a pretty sorry looking graph, looks more like a hi pass filter than a speaker.

I wish I knew what a real SO is supposed to be like!I did not think about your woofer size when I noticed the size of the slot.It you lay the thing on its side it makes a noticible differance with my hack. I also fire the horn into a corner and the output is higher on the horn than the front where the speaker and slot is. That gives me two sides of extention with it on the floor fireing into the corner (kinda) and a top. When the top is on and its standing up its output is minimal.I tried it again on its side with the top off and the horn fireing into the corner and it makes a big diff.

My FS/QTS is the exact opposite of the spectrum. I sure would like to know what specs the thing is designed for.

Have you tried covering up the slot and firing into a corner? My standard Imperials are indicating that the direct speaker radiations are actually reducing output when the Imperial is firing into a corner. In other words the Imperial firing into a corner does better with no direct speaker radiation going into the corner too. Are you seeing the same thing?

sorry DankMy hack is a corner cab. the horn exit is at the top and the normal corner cab has a flat lid so to speak.I when I used it against a wall with the lid on ( it was in the middle of that wall) it was really week and I could hear it but not that get your attention bass.I took the lid off ( the top of the corner cab) and laid it downon the floor with the opened horn exiting into a corner behind my corner TV stand.The slot was facing into the room about 2 feet away from my TV stand.The output was substantially better. And yes mine seems to have more output through the horn than the slot. when I stick my head into the horn i readilly hear bass. but when i put my head near the slot the bass is less pronounced.I would not compare mine to yours because mine was based on what I had thought a SO would be like in a smaller form to fit where I wanted it to.Mine ended up working better than I thought but I still want to know what makes up Steves Imp SO.I presently am looking for an addtional amp to power it in my garage to give it a good healthy run.I will try to post a pic of its intended placement ( untested there at the moment)

High QTS normally means sealed box or open baffle. Since the SO is a horn resonator built around a sealed box, my guess is high QTS is good. The thing to watch is how a given driver works with the volume the SO has in its sealed chamber. If it is too big, no problem, add bracing. If there isn’t enough volume, the speaker’s low-end extension will fall off.

I'll just wait for the plans. If I wanted to do try one on my own, then I'd go radical and use the open slot loading for the horn and forget the sealed chamber. ei open baffle bass with horn loaded support of the bottom end. No 5 cube chamber, with a corner to form the final horn flare.....hmmm...OB with horn support on the bottom end where OB rolls off, all in a compact form. That has potential to be a perfect sub.

[quote author=dank link=1129662594/0#12 date=1129847111]The speaker I’m using doesn’t seem to model well in a sealed 5 cubic foot box (if I’m using the s/w correctly). Perhaps some nice person out there can check my results to see if I’m doing it right. Fs = 30.5 hz, Qts = .227, Vas = 8.6 cubic feet, 8 ohm, 18” diameter. When I model it in a sealed box of 5 cubic feet my s/w says Fc = 50, Qtc = .37 and Cutoff(F3) = 116. [/quote]Your numbers look good to me. I do not have software, only a table of values in a book which only go down to Qtc 0.5. Setting Qtc to 0.7 I calculated f3 = 94Hz, Vb = 1.0 cu ft.With Qtc 0.5, f3 = 103Hz, Vb = 2.3 cu ft. I think your numbers would extrapolate from these. If your cabinet has a door to give access to the sound chamber, you might throw in some sand bags to reduce the volume to 1.5 cu ft or smaller. This might improve your bass without having to buy a new driver.

I finally re-worked my front panel and tried a couple different 15" drivers, rather that the 18" that was originally installed. All to no avail, as I'm still getting virtually zero output from this thing. Here are some pictures:

It's from Steves plans. The only modification is that it has a hole for an 18" speaker rather than a 15", and the way it's setup now is theres a 15" speaker installed on an adapter board.

It has to be serious cancellation, thats the only thing it could be, right? I see the speaker cone moving like crazy, but there just isn't much sound. If I cover up the front slot opening its quite a bit louder, but thats the only thing I can do to make this sound better: cover up the front entirely.I did send a full range signal through it yesterday and it had good volume in the vocal range, just no bass. I think that proves cancellation in the lower frequencies.

This may be a silly question, but I think it's time to cover all the bases. Do you have some other bass speaker to use as a reference standard to verify that your hearing is not damaged in the bass region?

A graph of actuall response like a meter away would work too. If it is indeed cancelation(which I expect is the case.), the graph would gradually slope down to the perfect cancelation frequency then begin to slope upward as frequency goes down further.

Kinda like a normal response with a large dip in the frequencies surrounding the cancelation frequency.

Also, this graph would show exactly what you are trying to describe, or wether there is output or not.

Looking at the graphs in pairs, i.e. 3 and 4 or 6 and 7. The response in the bass region is practically the same with or without the front baffle on. This would lead me to assume the k slot isn't loading the speaker's front wave into the horn portion at all.

so your K_slot is either, a) not working properly or b) the sealed portion of the box is what is causing the reduced lower output.

Okay, i actually figured out what the problem is.

Spec wise, the JBL and the Cerwin Vega are vented box only subs, the barely reach into the 80 hz range when sealed. I assume the madison one is also since I couldn't model it.

The reason the subs work fine in a normal imperial is the fact that there is no sealed chamber.

[quote author=J_Rock link=1129662594/30#30 date=1138750730]Spec wise, the JBL and the Cerwin Vega are vented box only subs, the barely reach into the 80 hz range when sealed. I assume the madison one is also since I couldn't model it.

The reason the subs work fine in a normal imperial is the fact that there is no sealed chamber. [/quote]

I can remember Steve saying you need a driver that can get into the 20's in a sealed cabinet. I know the JBL won't do that without copious amounts of EQ'ing. You mat be onto something J_ROCK.

I don't think that the sealed area is the problem.I think J rock may have it.As far as we know Dank has built it correctly and is an experianced builder. So the K slot is out as well as the sealed area.

That would leave the type of driver suspect.In my hack I built the sealed area around the driver specs and the driver specs were 25Hz in a sealed enclosure.

When I converted my So into standard Imp configuration the output was greater in volume.

I have a pair of 12"s that will do 20Hz in a sealed enclosure but I can no longer test that theory because my last mod is not reversable.I have no idea if that is of any help but I thought it was worth mentioning.

At the present I am using the IMP hack on its side as a sturdy table for some other projects. as some may remember it is reinforced carboard and the sealed chamber was wood ( now the Compression chamber).

It may sound strange but for me it has much more output than usable and it's too big.

I don't think I need an Imperial even if I did have the room. if my hack works that well, I have no need for a real Imp sub that will most likely blow mine away.

The Imperial SO is being driven with a signal generator through an amp. The slp meter is a Radio Shack unit about a meter in front of the Imperial SO. I had a volt meter and current meter hooked up and calculated the power going to the speaker at each frequency, as well as recording the slp. Since the power was all over the map, I took (10 log power) and used that to normalize the slp meter reading. That is what the graph uses: the normalized slp vs frequency from 20 hz to 250 hz.

I find it VERY hard to believe that a JBL E-140 would preform so poorly in a 5 cubic foot sealed cabinet. This speaker produces close to 100 db (1w/1m) when sitting on a sealed standard volume box (3 cubic feet) that I use for measuring speaker parameters. Now its producing 65 db (1w/1m) at 60 hz?? Thats barely above room ambient!!! I just can't believe that every speaker I've tried (there have been at least 4 different ones) is that much of a mis-match.

Or at least until I get a spare PC set up in my garage.I have a bunch of old 68Kmacs stiing around but no audio software that old.( So on a side note if anyone knows of any old Macintosh 68K pre PowerPC audio software out there let me know)

Anyway this is my wierd side speaking:what would happen if you shimmed up the horn without taking the whole thing apart.sliding a sheet of 1/4 ply up the back of the inside and making the whole horn shallower in a way. as a temp way to change the horns tuning.so just changeing the horn tuning without taking the whole thing apart.Would that accomplish anything?Or would it because you had sealed off the front and the diff was marginal.

and a stupid question, the chamber behind the driver is completely sealed right?

When you get this figured you are going to start a new thread (Imperial SO problems solved) and detail the problem or at least let us poor saps that are trying to help know what is going on.

I am still waiting for the plans to show up on line just to have them.

I don't know that the sealed chamber is the problem, But I do see it being one of few possibilitys. The original imperials were ported versions, and a driver like the jbl e 140 would do well, considering theres a single larger port firing into the horn.

I could only recommend trying a driver that excels in a sealed enclosure/ Perhaps you could give us a list of anyt drivers you would be willing to throw into the SO and we could suggest the best one. If you had specs on them too would be nice, since a few subs aren't in winISD and I would need to program them inorder to model them.

To J_rockYou might have something there. I did not see your yellow line in my graph, but it fits pretty well. I questioned the drop off rate though, until I saw it was 6 db/octave, its just that it goes on (and on and on) for about 4 octaves and 24 db.

Heres some more info...I boarded up the Imperial SO and re-did the frequency response the same way. Heres the graph:

Now this is the same speaker, in the same 5 cubic foot sealed enclosure, its just that now its only firing into the horn. These slp numbers are more like what I'd expect.

One last thing I noticed is that since I had the V and I figures for the different frequencies, I also had the speaker impeadance. When I graphed this it came as a surprise to me. Maybe it will give someone out there another clue as to whats going on. Here are the 2 graphs:

I have a couple dozen build pics that I will move up to the web tonight and post links to. Lets see if you can spot anything.

As far as mods go, its for an 18" instead of a 15" and I didnt have the ImperialSO.gif drawing when I built it so none of the brace B's, brace D's, or brace E's are in it. Also the origional front panel cutout was cut too big, so I made a new front panel just recently...so a couple of the build pics will have the old front panel.

I could be completely wrong but my guess is the sealed chamber isn't allowing the subs to move air. Too high of a compliance.

I mean, if the driver can't produce reasonable output in the sealed chamber, theres no output for the horn to amplify...

I hope its something other than the subs though.

Perhaps Zigi could give us the name of the drivers in chnageouts, to see how they model in a sealed enclosure. If they model as poorly as the JBL's do, they we could deduce that the sealed volume is not what is impeding the output.